1. Field of the Invention
This invention relates generally to telecommunication systems, and, more particularly, to wireless telecommunication systems.
2. Description of the Related Art
The list of devices that use wireless communication techniques, such as a cellular telephone system, to transmit voice and data signals has expanded dramatically in recent years to include, among other things, cell phones, personal data assistants, global positioning system receivers, laptop computers, and desktop computers. And the number of devices on the list, as well as the services they are likely to provide, is expected to continue to grow. The proliferation of wireless communication systems has led users to expect to access these systems at virtually any time and in virtually any place.
Wireless telecommunication systems, such as cellular telephone systems, typically include one or more base stations that can establish concurrent communication links with one or more mobile units in geographic areas, referred to hereinafter as cells, associated with the base stations. The range of a wireless communication link is limited by the transmission power of the base station and mobile units, the sensitivity of receivers in the base stations and mobile units, obstacles between the base station and mobile units, and the like. Thus, while cellular telephone systems provide reasonably reliable service in open and/or outdoor environments, the quality and/or reliability of a cellular telephone connection between a base station and a mobile unit may be reduced when the mobile unit is used in or near structures such as office buildings, warehouses, and the like. Moreover, cellular telephony may not be supported in every location.
Alternative communication protocols have been developed to provide reliable, high quality communication networks in constrained settings such as building interiors. For example, the Bluetooth standard is commonly used to implement short distance wireless networks having a defined set of member devices, which are sometimes referred to as piconets. Bluetooth compatible devices transmit data and/or voice over an air interface, or wireless communication link, in the Industrial, Scientific, and Medical (ISM) frequency band at about 2.4 GHz using a frequency-hopping technique. Due in part to the frequency-hopping characteristics of the Bluetooth standard, the communication link formed according to the Bluetooth standard has a reasonable chance of maintaining link quality in the presence of interference. The Bluetooth standard is well known to persons of ordinary skill in the art, and so, in the interest of clarity, only those aspects of the Bluetooth standard that are relevant to the present invention will be discussed herein.
FIG. 1A conceptually illustrates a K3 cordless telephony profile stack 100, which may be used by mobile units and/or base stations to form one or more wireless telecommunication links according to a conventional Bluetooth protocol. Persons of ordinary skill in the art should appreciate that only those elements of the K3 cordless telephony profile stack 100 that are relevant to the present invention are illustrated herein. Voice packets are received by a telephony application 105, which provides the voice packets and other control signals to a Telephony Control protocol Specification Binary (TCS Bin) block 110. The TCS Bin block 110 generally functions by enabling a connection-oriented link between a terminal (not shown) and a gateway (not shown). The link is unique to the gateway and enables the gateway to host multiple TCS bins. In this manner, signals transmitted between the TCS Bin blocks 110 associated with different users can be discriminated. For voice services, a link identifier and an associated identifier (the SCO handle) identify the voice channel to the gateway.
FIG. 1B shows a conventional TCS Bin header 112 that includes a three-bit protocol discriminator field (PD) for discriminating internal messaging. A protocol discriminator 111 uses the TCS Bin header 115, which is typically attached or appended to each voice packet, to determine how the voice packets provided to the TCS Bin 110 are handled. The Bluetooth standard has explicitly defined three values for the protocol discriminator field (PD). A value of 0x0 in the protocol discriminator field indicates that a call control (CC) block 120 should handle the message, a value of 0x1 in the protocol discriminator field indicates that a group management (GM) block 122 should handle the message, and a value of 0x2 in the protocol discriminator field indicates that a connection-less (CL) block 124 should handle the message. All other values of the protocol discriminator are reserved in the Bluetooth standard. Once the TCS Bin block 110 has decided the recipient of the message, the message itself is identified by a five-bit type field (TYPE).
Referring back to FIG. 1A, the functionality of the TCS Bin block 110 is determined by the call control (CC) block 120, which provides ITU-T Q.931 call control functionality that is common to most types of cellular and fixed line telephony. The call control (CC) block 120 manages a voice channel via an interface 125 with a speech synchronization controller 115 and an interface 130 with a link manager protocol (LMP) block 135. For example, the call control (CC) block 120 may connect and/or disconnect internal speech paths by providing signals to the speech synchronization controller 115 via the interface 125 and may establish and/or release voice synchronization control links by providing signals to the link manager protocol (LMP) block 135 via the interface 130. The link manager protocol (LMP) block 135 is coupled to an asynchronous control block 137. The interfaces 125, 130 enable the speech synchronization controller 115 to directly control the voice path from the telephony application 105 to a synchronous controller 140 in a baseband 145. Thus, the telephony application 105 typically obtains guaranteed quality and/or delay characteristics.
A growing number of mobile units, such as cellular wireless telephones include both a conventional cellular telephone interface and a Bluetooth interface. Thus, a mobile unit may be able to place a wireless telephony call according to two protocols: a cellular voice protocol (such as UMTS, GSM, IS95, CDMA200, etc) and a Bluetooth protocol. Both the cellular voice protocol and the Bluetooth protocol provide inherent quality guarantees for the voice application and attempt to guarantee that the delay experienced by the voice traffic will remain below a predetermined level. The cellular voice protocol also allows a mobile unit to move from one cell to another. The Bluetooth protocol, however, does not allow for mobility outside of the mobile unit's current piconet. Moreover, only the call state is maintained and the Bluetooth protocol typically relies on an outside network connection for onward guarantees of the delay and quality. Examples of the outside network include a public switched telephone network (PSTN) home base station, an Integrated Services Digital Network (ISDN) home base station, a GSM gateway, a satellite gateway, and an H.323 gateway.
The present invention is directed to addressing the effects of one or more of the problems set forth above.